Control system



2 Sheets-Sheet 1 W. G. COOK CONTROL SYSTEM Original Filed April 25, 1939 Y INVENTOR l'x/z/iw'dfi' (700A: m gi);

ATTORNE June 1, 1943.

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June 1, 1943. w. G. COOK 2,320,850

- CONTROL SYSTEM Original Filed April 25, 1939 2 Sheets-Sheet 2 WITNESSES: 1NVENTOR IA/ZZZUI'CZ G 000/6.

ATTOR EY Patented June 1, 1943 2,320,850 CONTROL SYSTEM Willard G. Cook, Wilkinsburg, Pa., assignor t Westinghouse Electric & Manufacturing Company, East'Pittsburgh, Pa., a corporation of Pennsylvania Original application April 25, 1339, Serial No. 269,907. Divided and this application January 9.1941, Serial No. 373,855

6 Claims.

My invention relates, generally, to control systems and, more particularly, to control systems for maintaining a desired relation between the output potentials of a plurality of generators.

This application is a division of my copending application Serial No. 269,907, filed April 25, 1939, entitled Control systems and assigned to the Westinghouse Electric & Manufacturing Company.

In the operation of two or more associated work devices between whose speeds it is desired to maintain a desired relationship, it is common practice to drive one of the devices by a motor whose armature is energized by a continuouslydriven generator, the output potential of which is varied by varying its excitation in accordance with the speed of the other device. Thus as the speed of the second mentioned of these devices is varied, the armature energization of the first mentioned device is varied to vary the speed of the first device accordingly.

This method of maintaining the desired speed relationship between work devices has been applied to rolling mills where the reel motor or run-out table motors are energized by a continuously driven main generator, the excitation of the main generator being provided by a continuously excited pilot generator driven by the mill roll motor and thus exciting the main generator in accordance with the speed of the mill motor. It will be understood that the output potential of the main generator willbe proportional to the output potential 'of the pilot generator and the speeds of the reel motor ortable roll motors and the mill motor will have thesame relationship.

This system has the disadvantage however that during periods of acceleration and deceleration of the mill the potential of th'e'main generator does not maintain the proportional relationship with 'the potential of the pilot generator due to the fact that the main generator, being a relatively large machine, has a field winding of rel tively high inductance and this causes a considerable time lag between a given change in. the potential of the pilot generator and the potential of the main generator which is controlled by the potential of the pilot generator. Thus the desired speed relationship of the mill roll, reel, and table roll motors will not be maintained during acceleration and deceleration periods of a rolling mill controlled by this system;

It is the object of the invention, therefore, to provide a control system for aplurality of work devices which shall function to maintain a desired speed relation between the work devices regardless of the acceleration and'deceleration of the devices.

Another object of the invention is to provide a control system for a plurality of generators which shall function to maintain a predetermined selectable proportional relationship between ,the output potentials of the generators.

A further object of the invention is to provide a control system for a plurality of motors which shall function to maintain a predetermined sclectable speed relation between the motors.

These and other objects and advantages of the invention will be apparent from the following detailed. description taken in connection with, the accompanying drawings, in which like reference characters are used'to designate identical and similar elements of structure and in which,

Figure 1 is a diagrammatic view of a control system for a portion of a rolling mill embodying the principal features of myinvention, and

Figs. '2 and 3 are diagrammatic views of other embodiments of my invention.

In the embodiment of my invention shown windings to be energized by a pilot generator 34 driven by the motor 20. Field forcing of the generator 32 is provided by a pilot generator 38, which is connected to vary the excitation of the generator 32 in accordance with the diiierence between the output potentials of the generators 32 and 34.

In the embodiment of the invention of Fig. 2, the booster generator 36 is excited in accordance with the difference between the potential of the pilot generator 34 and that of a pilot generator 34' driven by the table roll motor 22.

The embodiment of the invention shown in Fig. 3 provides for simultaneous adjustment 0!.the field energization of the main generator 30 and the generator 32 which energizes the reel motor or the table roll motors, by means of a rheostat ii. The pilot generator 36 is excited in accordto control analogous parts of other similar work devices, and that any operative subcombination of any of the embodiments of the invention may be used in other systems where its function as herein described may be utilized.

Referring again to Fig. 1 of the drawings, the

rolls in of the mill are driven by the motor 20 to w act upon the slab 52, passing it-through the mill in the directionshown by the arrow. The motor 20, is energized by the generator 30 through the conductors 64 and 56. .The generator 30 is continuously driven by synchronous motor 58 or any other suitable driving means. The field winding 60 of the generator 30 is connected through a rheostat 62 to any suitable source of direct current power indicated by ,theconductors A-B. The rheostat 62 may be adjusted to vary the excitation and, therefore, theoutput potential of the generator 33. This variation of the armature potential of the motor 20 will vary the'speed of the motor 20.

The field winding 64 of the motor 20 is connected through a rheostat 63 to the conductors A-B. The base speed or normal speed range of the motor 20 may be varied by varyingits excitation by the adjustment of the rheostat 68.

The table roll motors 22, 24, 26 and 28 have their armatures connected in parallel circuit relation to be energized by the, generator '32 through the conductors and 12. The excitation of the generator 32 may be varied by adjusting the current fiow in its field winding I4 by means-of a rheostat 16. The generator 32 is provided with another field winding 16 which is connected to be energized by the output potentials or the pilot generator 34 and the booster generator 36. v The circuit for the field winding 13 extends from one side of the pilot generator 34 through the conductor 30, the booster generator 36, the conductor 82, the field winding lt, and the conductors 84 and 36 to the pilot generator 34.

The pilot generator .34 is provided with a field winding 68 which is connected in series circuit relation with a rheostat 30 to the conductors- A-B. The generators 32 and 36 may be conthe other side of seen that the output potential of the pilot generator 34 will vary directly with the speed or the motor 20 since the pilot generator 34 is driven by the extension of the shaft 8! of the motor 20.

As the speed of the motor 20 is varied by varying' the excitation of the generator 30, the pilot generator 34 will vary the potential applied to the field winding 18 of the generator 32 to thus vary the output potential of the generator 32 and vary the speeds of the motors 22,24, 26 and 28 accordingly.

However, the size of the generator 32 is such that its field winding 18 has a considerable in ductance, and there will be a time lag between the change of the potential applied to the field winding 78 due to the change of the output potential of the pilot generator 34 and the corresponding change in the-excitation of the generator 32 to produce a corresponding change in the output potential of the generator 32.

During the interval of this time lag the output potential of the pilot generator 34 will increase faster than the output potential of the generator 32, and there will thus be a corresponding change in the difference in these potentials. Since. the booster generator 36 is connected to be excited in accordance with the difference of tinuously driven by the motor 58 through an extension of its shaft 3|. The booster generator 38 .is provided with a field winding 92 which is energized in accordance with thedifierence in the output potentials of the generators 32 and 34, the field winding 32 being connected by conductor 94 to one side vof the generator 32 and by conductors 96 and to one side of the pilot generator and the other side of the generators 32 and 34 being connected together by the condoctor 66..

In the operation of the system of Fig. 1, the excitations of the motors 20, 22, 24, 26 and 26 may be so adjusted as to provide the desired tween the meters 20, 22, 24, 26 and 28 as will result in equal peripheral speeds of the rolls Ill and the table rolls l2. l4, l6 and I6. Itwill'be the potentials of the generators 32 and 34, the

output potential of the booster generator 36 will more nearly simultaneous increase of the output potentials, of the pilot generator 34 and the generator 32 and accordingly, the simultaneous proportional changes in the speeds of the motor 20 and the motors 22, 24, 26 and 28.

In the embodiment of the invention shown in Fig. 2, the pilot generator 34' is driven by the ductor I58, the armature of the pilot generator 34, conductor 80, the. field winding 92 of the booster generator 36, conductor 160, a rheostat I62 and conductor I64 to the other side of the pilot generator 34'. With this circuit it will be seen that the field winding 92 of the booster generator 36 will be energized in accordance with the difference between the output potentials of the pilot generators 34 and 34' and the output potential of the booster generator 36 will also vary in. accordance with this difference. Since the output potentials of the pilot generators 34 and 34' are proportional to the speeds of the motors 20 and 22, any variation from the desired relative speeds of the motors 20 and 22 will be compensated for by a corresponding variation of the excitation of the generator 32, thus adjusting the speed of the motor 22 by adjustment of its armature potential.

In the embodiment of the invention of Fig. 3, simultaneous variation of the speeds of the motors 23 and 22 is provided by the actuation of the rheostat ii to vary the energimtion of the generators 30 and 32 which energize the armatures of the motors 20 and 22, respectively. The rheostat 5! comprises a variable resistor I connected in the energizing circuit of the field winding ill of the generator 3. and a variableresistor I62 connected in the energizing circuit of the field winding 13 of the generator 32. The variable resistors I66 and I68 are mechanically connected to be simultaneously actuated by an operating handle The booster generator 26 is also connected in circuit with the field winding ll of the generator 32 and has field windings I12 and I14. The field winding H2 is connected to be energized by the output potential of the generator 32 in series with an adjusting rheostat I16. Similarly, the

field winding I" is connected to be energized by the output potential of the generator 32 in series circuit with an adjusting rheostat H8. The field windings I12 and H4 are connected to D- pose each other, so that the net excitation of the booster generator 36 will vary in accordance with the diiference in the output potentials oi the generators 30 and 32.

In the operation of this embodiment of the invention, when it is desired to change the speed of the motors 20 and 22, the rheostat 5| is operated, as hereinbefore described, to vary the energization of the field windings oi the generators 30 and 32 and to thus vary their output potentials. If, however, due to the inductances of the field windings 60 and I8, the output potentials of the generators 3|! and 32 do not vary corresponding amounts, the variation of the difierence of these potentials will cause a variation in the excitation of .the booster generator 36 which, in turn, will vary the energization of the field winding ll of the generator 32 to thus tor-cc" the field of this generator to compensate for the variation in the difference in the potentials of the generators 30 and 32.

It will be seen that I have provided a control system for a plurality of work devices which shall function to maintain a desired speed relation between the work devices regardless of the acceleration and deceleration of the devices, which may be adjusted as desired to vary such speed relations, and which shall be simple in operation and inexpensive to manufacture, install and maintain.

In compliance with the requirements of the patent statutes, I have shown and described here in the preferred embodiments of my invention.

It is to. be understood, however, that the invention is not limited to the precise constructionsshown and described but is capable of modification by one skilled in the art, the embodiments herein shown being merely illustrative of the principles of my invention.

I claim as my invention: I 1. In a control system for maintaining predetions of the speeds of the motors.

termined speed relations between a pair of motors, a separate variable potential generator energizing each of the motors, a booster generator connected to vary the excitation of one of said generators, and means applying a net excitation to said booster generator proportional to the differences between quantities which are func- 2. In a control system for a pair of motors, a main generator connected to energize one of the motors, a first pilot generator driven by the other motor for exciting said main generator, a booster generator also connected to excite said main generator, a second pilot generator driven by said one motor, and means for exciting said booster generator in accordance with the dinerence between the output potentials of said first and second pilot generators.

3. In a control system for a pair of motors, a main generator connected to energize one of the motors, a first pilot generator driven by the other motor, a booster generator, means connecting said booster generator, said first pilot generator and the field winding of said other motor in series circuit relation, a second pilot generator driven by said one motor, and means connecting said first and second pilot generators and the field winding of said'booster generator in series circuit relation.

4. In a control system for a pair of motors having individual main generators connected to energize their respective armatures, a booster generator connected in series circuit relation with the field winding of one of the main generators, and means connecting the main generators to excite said booster generator in accordance with the output potentials of the generators, and

means for simultaneously varying the excitation of the main generators.

5. In a control system for a pair of motors, a main generator connected to energize each of the motors, means for simultaneously varying the excitation of said main generators, a booster generator connected to affect the excitation of one of the main generators, and means exciting said booster generator in accordance with the difference between the output potentials of said main connecting each of said booster field windings to be energized by the output potential of a separate one of said main generators, and means for simultaneously varying the excitation of the main generators.

WILLARD G. COOK. 

